The lead-acid secondary battery is used extensively as a source of power for starting automobile and other engines, as a constant voltage source and as a source of power for emergency use. For many of these uses this battery has proved quite satisfactory. It is relatively cheap, durable and responds to a variety of power demands. Its lifetime is usually limited to a few years but for many applications this is satisfactory.
One use of lead-acid batteries which is becoming increasingly important is as a standby source for emergency power use. Typical standby uses are in telephone equipment and computers to provide temporary power at power outages and to start power generator systems. In this application large power capacities are required but demand for this power is usually relatively infrequent. In order to obtain large power capacities from batteries, a relatively large initial investment is required.
The failure mechanisms usually present in continuously or frequently used lead-acid batteries are often not present in lead-acid batteries employed for standby, emergency use. Many failure mechanisms for lead-acid batteries depend on the extent of use. For standby batteries that are infrequently used, such failure mechanisms that depend on use are often not important. For this reason, standby lead-acid batteries often have longer lifetimes and different failure mechanisms from frequently used batteries. It is highly desirable to minimize or eliminate failure mechanisms characteristic of infrequently used lead-acid batteries so as to maximize the useful lifetime of such standby lead-acid batteries.
Lead-acid batteries have a large variety of seals between conducting parts and insulating parts. A particular example is the seal between the positive battery post and the casing in a lead-acid battery. High reliability and long life are highly desirable in such seals. A large number of seals have been described in the literature. Particularly interesting are a series of seal designs disclosed in U.S. Pat. No. 3,434,883 issued to L. D. Babusci et al on Mar. 25, 1969 and U.S. Pat. No. 3,490,954 issued to L. D. Babusci et al on Jan. 20, 1970. These references describe a much improved seal design for lead-acid batteries. Such designs depend on good adhesion between the battery post (or at least a conducting part of the battery) and the battery jar or nonconducting part of the battery. A particularly useful post seal which is convenient to manufacture in large numbers is described in U.S. Pat. No. 3,652,340 issued to L. H. Sharpe et al on Mar. 28, 1972.
Long-lasting, reliable seals are particularly desirable for the positive post of lead-acid batteries. Here, adhesion to the positive post is often more difficult for two reasons. Electrochemical action at the positive post tends to cause corrosion. The same electrochemical action may also prevent adhesion of sealing substance to the post material. Long life for such positive post seals are highly desirable for lead-acid batteries made for standby use such as those described in U.S. Pat. No. 3,434,883 issued to L. D. Babusci et al on Mar. 25, 1969, U.S. Pat. No. 3,532,545 issued to L. D. Babusci et al on Oct. 6, 1970 and U.S. Pat. No. 3,556,853 issued to A. G. Cannone on Jan. 19, 1971.